1. Field of the Invention
The invention concerns a process for purifying and reusing surfactant-containing waste waters from washing processes.
2. Description of the Related Art
The purification and reuse of surfactant-containing waste waters, in particular those such as produced by laundry facilities and car washes, as well as surfactant-containing waste waters from private households, represented technological challenge, since surfactants by nature present an extremely disruptive environment for organisms of all types, in particular the microorganisms of a mixed bioecology.
Above and beyond this, the industrial waste waters from a laundering process, in particular laundry waste waters or waste waters from car washes, comprise chemically relatively complex mixtures, which are extremely difficult to purify or to render reusable.
In particular, the waste waters from laundries are obviously strongly dependent in their quantitative and qualitative composition upon the detergents employed for the washing or as the case may be cleaning processes. Since universal detergents are primarily employed in the laundry facilities, the composition of the effluent is determined primarily, besides the textiles to be cleaned and the specific impurities contained therein, essentially by the composition of these universal detergents.
This type of universal detergent is comprised as a rule of an abundance of chemically varied substances, in particular anionic and non-ionic surfactants, fillers, compatibilizers, bleach agents, bleach activators, color preservers, corrosion inhibitors, stabilizers, anti-foaming agents, enzymes, optical brighteners as well as carriers and additive agents.
As anionic and non-ionic surfactants there can be mentioned for example alkylbenzolsulfonate, alcohol sulfate as well as alcohol ethoxylate.
As carriers generally zoelite A, sodium triphosphate and sodium carbonate are used. There is however an increasing modern trend for ecological reasons to avoid the use of phosphates and to replace these with ziolite and/or other silicates.
This type of carrier or filler is necessary, in order to enhance by a multiple the cleansing effect of the surfactant. In particular, the fat removing properties of the detergent or cleansing materials are strongly enhanced by the use of the fillers.
As co-fillers frequently a polycarboxylate is primarily used.
As bleaching agent, perborate, in particular sodium perborate as well as tetra acetyl ethylene diamine are used as bleach activators.
As fade inhibitors one employs mainly carboxymethylcellulose or, as the case may be, cellulose ether.
As corrosion inhibitors primarily alkaline silicate is employed.
Phosphonates serve as stabilizers and soaps, silicon oil and/or paraffin serve as foam inhibitors.
As enzymes primarily proteases and amylaces and sometimes however also lipases can be employed.
Above and beyond this, frequently optical brighteners comprised of stilbene or biphenyl distyryl types are employed.
Besides color materials, aromatic materials which can be added as a further ingredient frequently include sodium sulfate as a filler material or as the case may be as a production facilitating material.
The use of powder type universal laundry detergent in laundry facilities is experiencing increasing resistance to phosphates as ingredients and these phosphates are being replaced substantially with ziolites, soaps, citrates and amines, in particular tri- and monoethanolamine.
In particular, practically only phosphate-free laundry materials are being employed at this time in the United States and Japan as well as in the Netherlands, Germany, Switzerland, Austria and Italy and therewith in the effluent foam from laundry facilities.
In car wash facilities however a series of other substances end up in the effluent, for example, those which can be selected from: care substances for automobiles in particular waxes such as natural waxes or polyethylene based waxes, polishing substances; fatty substances; creams, in particular silicon fats, silicon oils, motor oil, transmission fluid, fuel, in particular gasoline and diesel fuel; antifreeze materials, in particular glycol; aminoxide; quaternary ammonium compounds; betaine; dialkyldimethyl ammonium salts, in particular chloride; rock salt; as well as mixtures thereof.
As a result of the above described complex composition of surface active agent (surfactant) laundry and cleansing solutions it follows that the chemistry of the respective effluent is extremely complex. As a result of legal requirements and ecological prohibitions the disposal of surfactant containing cleansing solutions in canals or sewage systems is in general to be avoided as a method of disposal. The manner of the treatment process and required investment are directly related to the respective type of treatment and the local regulations or as the case may be the discharge water laws. Acids or alkali cleansing materials must be neutralized. When treating emulsified oils a separation of the emulsion is necessary. Usually the result of an emulsion separation is that the oil content is not reduced to the prescribed legal limits, so that a subsequent flocking with aluminum or iron salts, frequently with supplementation of flocking assistants, must occur. With silicon-containing detergent solutions the salicylic acid which precipitates as a result of the neutralization causes an adsorption of oils and other organic substances.
In a waste water pre-treatment the surfactants found in the solutions are in large part removed along with the separation of the oils and fats insofar as they are oil soluble.
During the precipitation or as the case may be flocking of aluminum or iron phosphates or as the case may be hydroxides the chemical oxygen demand (COD-value) of the waste water, which is the most important factor in the determination of the waste water release, can be strongly reduced, insofar as the surfactants or also other adsorbable organic substances are brought out.
A further treatment possibility for the surfactant containing detergent solutions is the expensive and labor intensive ultrafiltration.
In the ultra-filtration there occurs, besides the effort and costs for the ultra-filtration membrane, the problem that though oil soluble non-ionic surfactants and anti-foaming materials are almost completely retained, water soluble non-ionic surfactants however almost completely pass through the membrane. With anionic surfactants there is established in comparison an equilibrium between membrane transmissive and retained surfactants (Kosswig/Stache, "The Surfactant" Carl Hanser Publishers Munich; Vienna (1993)).
The treatment of laundry waste water by ultra-filtration is extolled for example in DE-A 35 13 940, in particular for reclaiming of water and unspent wash active substances. This type of ultra-filtration system incurs however a high investment and maintenance cost. Above and beyond this the surfactants frequently lead, particularly after long use, to a disruption or damaging of the ultra-filtration membrane.
Beside the investment and maintenance expense for ultra-filtration systems, the above described effect results in only an incomplete retention of the surfactant and thus to a high surfactant containing effluent, which may not be disposed of in the canals.
A likewise quite expensive process for treatment and reuse of laundry and rinse waters is disclosed in DE-A 41 24 915. This laid open patent application teaches that a portion of the surfactant containing effluent water should be filtered and a part of the effluent should be treated by floatation for reclamation of rinse water.
This process is represented on the one hand as avoiding the problem of salting of the water. On the other hand, a demineralized-thus expensive, desalinated fresh water reclaimed through ionic exchangers out of the effluent water is added back as cleansing water, so that a moderate salt concentration results.
Preferably metal salts are employed as the floatation assistants in this technique representative of the state of the art.
Therewith this state of the art process has the disadvantage that the floating sludge resulting from the floatation process must be taken care of.
Beyond this the waste water is treated by pressure tension floatation, which again is associated on the one hand with a technical investment and on the other hand with a relatively high financial investment and maintenance cost.
A further possibility for carrying out the floatation according to the teaching of DE-A 41 24 915, lies in the carrying out of a so called electro-floatation in place of the metal salt treatment. This however is burdened with the disadvantage that an electro-floatation facility is relatively expensive and in addition does not solve the problem of how to take care of the resulting surfactant containing floatation sludge.
A further approach for the treatment of waste water, as occurs after the washing of clothing articles in large laundry facilities, is disclosed in DE-A 40 35 433. According to the therein disclosed process, the oil-in-water emulsion produced by large laundry facilities is separated out with the organic solvent perchloroethylene, in order to separate the waste water into a first, essentially aqueous fraction containing a small amount of oil fluid, which by ultra-filtration is separated out into water and disposable oil, and a second solution fraction, which is the phase containing the surfactants and oil, which by distillation is resolved into a disposable oil-impurity mixture and the solvent.
This process according to the state of the art exhibits however the substantial disadvantage, that it is associated with the utilization of an eco-toxicologically disadvantageous organic solvent, which ultimately enters into the environment certainly at least in trace amounts. On the other hand there is at least a necessity for carrying out an ultra-filtration step, which as discussed above is associated with disadvantages.
Further there is described in DE-A 33 05 238 a process for biological cleansing of water following a preliminary clarification with a pre-filter, wherein the water to be cleansed circulates in its own filter cycle. Beyond this there is accomplished by the filter circulation also the aeration or, as the case may be, the oxygenation by means of an air driven mammoth pump. The objective of DE-A 33 05 238 is comprised therein of providing a capable filter, which no longer needs to be cleaned under normal operating conditions, and with which an automatic separation of the accumulating sludge, dirt, and the like is possible. On the basis of the design of the filter described in this document as well as on the basis of the oxygen enrichment of the water in the filter, such a filter type is typically proposed for use as an aquarium filter.
It is further noteworthy that this kind of filter can be employed in intensive fish breeding. This is due to the fact, that the filter is comprised of a combination of biological filter and large dirt particle filter, since lava gravel is employed as the filter material.
This aquarium filter according to the state of the art of DE-A 33 05 238 can be associated with a downstream active charcoal filter for absorption of non-decomposable substances.
Although according to DE-A 33 05 238 the aquarium filter described therein should be capable of treatment of effluent waters from laundry facilities and other wet works as well as for treatment of industrial waste waters, there are however no references with respect to the type of waste water, in particular the relationship of surfactant containing waste water in respect to the bio-ecology mixture.
According to Kosswig and Stache, "The Surfactant", Carl Hanser Publishers, Munich Vienna, 1993, among the synthetic compounds the surfactants represent a special case for the transforming organisms--which as a rule are bacteria. Surfactants are namely substances which are active upon the interface surface. In comparison to other organic compounds which are dissolved in water, these are especially active upon the interface or surface. This applies also for cellular membranes. This fact is what facilities the purely physical substrate--organism (enzyme)--contact. It intensives however at the same time the effect of these compounds which in other context are desirable, namely the dispersion of lipids. The cytoplasmic membrane of the bacteria and other microorganisms are comprised of phospholipids, which are bound to a protein complex. The lipid layer is comprised of an asymmetric biomolecular film of triglyceride and phospholipids, of which the hydrophobic ends are oriented inwardly and which hydrophilic ends are directed outwardly facing the protein layer. From biochemical research it has become conventionally understood, that surfactants have a solublizing effect upon the membrane lipids when they reach a necessary minimum concentration on the cellular outer surface. In this way openings result in the membrane, which make possible an exodus of cytoplasm. This phenomena is exploited for example for the isolation of DNA from prokaryotic and eukaryotic cells.
The problem of the biological purification process for surfactant containing waste waters can also be recognized by the fact that the methods prescribed by the European Community for determination of the primary degradation of surfactants, the so called OECD-Screening-Test or, as the case may be, the OECD-Confirmatory-Test is based upon a test duration or period of 19 days in the Screening-Test and with a test duration of 21 days in the Confirmatory-Test.
According to the OECD-Screening-Test, surfactants, which after 19 days are at least 80% degraded, qualify for being classified as biologically degradable.
For this reason there has until now been no biological process for purification and reuse of surfactant containing waste waters.